Strange and stranger....

But first, @ Dan Whiteside: thanks for the input on this. Later I'll do some testing and will try that to see if there's any result.

And now: the second dual core has the same problem... so I take the file to a third computer, one which I use for serious programming. It's an old faithful... and guess what? That render works here. It's an older machine, AMD Athlon XP 2400+, 2 GHz.

But now this is my suspicion:
  The dual cores were probably rendering, but the AA percentage counter was not updating. Why I think this is because on this older machine, as soon as I loaded the file and Bryce came up, it continued at 20%. From 0% to 20% in like.. an instant. Is possible if it's just a black background, but there's stuff there which would've taken a little bit of time. Furthermore, I have rendered a similar image (same one but with less objects) and I'm familiar with the speed it took to render AA between 0 and 20%.

  So I think the AA percentage update counter wasn't refreshing, yet the AA was progressing. There wasn't any render line either. I might be wrong and that no rendering was occuring... hard to know without better testing. Since the challenge date is getting close, I'll leave the testing for later.